I do not think that becoming lucid prevents any reactions. Though you may be able to control anything in your dreams, perhaps your actions can still affect your soul or your subconcious depending on what you believe. If any negative steps are taken, then maybe they will prevent you from reaching enlightenment in this lifetime, and you will be reencarnated and forced to live samsara yet again. Though most here probably dont agree with me, i think that everyone has a soul which is a peice of the ultimate truth of the uncreated knowlege. If you read past that mumbojumbo, then what i am trying to say is that if you have a soul and your soul is on an alternative spiritual goal just as you have a goal in the physical life, then i can see that any negative things you do in dreams will affect you just the same. Though believe what you want.